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Projection Vectors Problem

  1. Feb 25, 2013 #1
    1. The problem statement, all variables and given/known data
    The angle between two vectors a and b is ∅, where ∅≠90°. Under what conditions will |Projab|2 + |Projba|2 = 1?

    2. Relevant equations
    |Pab|= |[itex]\vec{a}[/itex][itex]\bullet[/itex][itex]\vec{b}[/itex]|/|[itex]\vec{b}[/itex]|

    |Pba|= |[itex]\vec{a}[/itex][itex]\bullet[/itex][itex]\vec{b}[/itex]|/|[itex]\vec{a}[/itex]|

    3. The attempt at a solution
    I know that |Pab|=|Pba| when |[itex]\vec{a}[/itex]|=|[itex]\vec{b}[/itex]|

    I'm not sure where I go from there.

    Any help is appreciated, thanks.
  2. jcsd
  3. Feb 25, 2013 #2


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    Looks to me like they just want you to derive an express for cos(∅) in terms of |a| and |b|.
  4. Feb 25, 2013 #3
    I think it's a little more complex than that. I am a little confused on what the question is asking though.
  5. Feb 25, 2013 #4


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    I worked through it and that's the only thing I can figure they could be asking.
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